It was a warm, spring day and a neighbor and I were watching some dogs charging around playfully in a fenced, dog-park area, seemingly oblivious to the heat. My neighbor commented, “You know, if we were running around like that we would be drenched in sweat. Dogs must be marvelously adapted to handle the heat.”
In truth, dogs are designed to handle cold better than heat. For humans, our major method of keeping cool is through perspiration. As our sweat evaporates, it results in a cooling effect, which lowers our body temperature.
Dogs have two types of sweat glands: merocrine glands (similar to human sweat glands) and apocrine glands. Merocrine glands are not widely distributed as they are in people but are mostly found in the paw pads. Sweating through their paws helps dogs cool down, at least a little. The apocrine glands are located throughout the body, and these also produce sweat in dogs, but this type of sweat doesn’t serve a cooling function. Rather, apocrine sweat contains pheromones, which are scent cues that convey information about the dog and help dog-to-dog communication.
The major way in which your dog cools down is through panting. This is his primary means of thermoregulation (an animal’s ability to keep his body temperature within safe boundaries). When your dog needs to cool down, his tongue may hang out of his mouth and his breathing will speed up. Dogs have a typical resting respiratory rate of 15 to 30 breaths per minute, but this rate can get significantly faster when panting. Panting moves the hot air in and out, and that airflow increases moisture evaporation from the mouth, mucous membranes of the nasal passages, and lungs. This effectively cools the body from the inside out.
The hotter your dog is, the faster and harder he may pant. You may have noticed that sometimes your dog will pause in his panting to take a deep breath, and then return to short, rapid breathing. That’s because panting is not an effective way of exchanging air in the lungs. The panting pause occurs because your dog is taking a large breath to maintain oxygen levels in the blood.
Dogs have another interesting and unique way to help them cool down and this is through a process called vasodilation, where the blood actually seeks to cool itself. The process involves the blood vessels expanding and rising toward the skin level where the external air can then cool the blood before it returns to the heart. Vasodilation occurs mostly in the face and ears.
Dogs have behavioral tricks they use to keep cool. Obviously seeking shade is helpful, as is stretching out flat on a tile floor, looking like a pelt with their belly to the ground and their paws splayed out. The fur on the dog’s belly is thinner than the fur on the upper part of his body, so the cool ceramic floor helps lower his body temperature. In the absence of a cool floor, dogs may roll over onto their backs, exposing their underside. It’s another way to take advantage of that thin belly fur, since it gives a chance for the cooler outside air to draw away some of their internal body heat.
Unfortunately, none of these canine cooling methods are as effective as sweating is for humans. This means that dogs are at risk of heat stress and, more dangerously, heatstroke, as the body temperature rises to life-threatening levels.
The best strategy is to simply avoid situations where your dog might overheat. That means keeping your dog indoors during the hottest parts of the day and making sure that he has lots of water to drink. Cooling mats, vests, frozen water bottles in your dog’s crate, and crate fans can help cool your dog while on the road or at dog-sport events. One of my favorite tricks is to freeze an ice cube tray full of chicken bouillon and toss one of these frozen “pupsicles” to my dog to help keep him cool and hydrated on hot days.